SEOUL (Reuters) - U.S. charges that North Korea helped Syria build a nuclear reactor are not expected to derail international talks aimed at ending the communist state's own nuclear arms programme, a South Korean official said on Friday.

The United States on Thursday released photographs it said linked North Korea to a plutonium-producing reactor under construction in Syria in an effort to put pressure on Pyongyang to come clean about proliferating nuclear technology.

"There probably won't be much of a meaningful impact on the six-party talks," said a South Korean official familiar with the multinational negotiations.

Japan, however, said the charges were serious, if true.

"Of course, if North Korea was helping Syria's secret... nuclear activities, then this is a serious issue. I think it is important that this be made clear through the Six-Party Talks' correct and full declaration process," Japan's Chief Cabinet Secretary Nobutaka Machimura said.

Under the deal North Korea struck with five regional powers, it had until the end of 2007 to give a complete list of its fissile material and nuclear weaponry as well as answer U.S. suspicions of enriching uranium for arms and proliferating technology.

A U.S. envoy was in Pyongyang this week to advance the sputtering nuclear talks that have hit a snag over the declaration issue.

If North Korea, which tested a nuclear device in Oct. 2006 with plutonium produced at its Soviet-era reactor, makes the declaration, the United States will remove it from a terrorism blacklist and allow Pyongyang to tap into international finance.

Asked if the latest U.S. claims would an impact on the question of North's removal from Washington's list of nations that sponsor terrorism, Japan's Machimura said: "I don't think this would have a positive influence on North Korea."

North Korea, which lists Syria as one of its few close allies with diplomatic and civilian exchanges, has yet to comment on the new U.S. claims, but it has denied any involvement in nuclear proliferation, calling the Syrian nuclear connection "fiction."

Israel destroyed the reactor in a Sept. 6 air strike that was initially shrouded in secrecy out of what U.S. officials said was fear that public discussion could prompt Syria, which has long supported militant Palestinian groups, to retaliate.

The U.S. announcement comes on the heels of new South Korean President Lee Myung-bak's first trip abroad since taking office where he had a summit at the Camp David retreat last week with George W. Bush. The two urged North Korea to meet its obligations in the nuclear deal.

(Reporting by Jack Kim in Seoul, additional reporting by Yoko Kubota in Tokyo)

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